feat: ProjectConfig API spec and ctx variable for automated rollbacks

[jessesuen]

Introduces the API spec for automated rollbacks in ProjectConfig CRD, enabled like the following:

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: my-project
  namespace: my-project
spec:
  promotionPolicies:
  - stageSelector:
      name: prod
    autoRollback: {}

New AutoRollbackConfig type:

• Defines if a Stage should automatically roll back to the last known-good (verified) Freight
• Rollback on failed verifications is always enabled when this config is present
• OnFailedPromotions bool field: optionally also trigger rollback when a promotion itself fails

New kargo.akuity.io/rollback annotation:

• Applied to Promotions that were created as rollbacks to previously verified Freight
• Used to derive the Rollback bool field in promotion context

Rollback context propagated through the promotion engine (ctx.meta.promotion.rollback):

  steps:
    - uses: xxxx
      if: ${{ !ctx.meta.promotion.rollback }}

• promotion.Context.Rollback — set from the annotation at context construction time
• promotion.StepContext.Rollback — passed through to individual step execution
• meta.promotion.rollback — exposed in the expr expression environment, allowing promotion steps to branch on whether they're running in a rollback

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.05%. Comparing base (9de13ee) to head (2c82d0f).

Files with missing lines	Patch %	Lines
pkg/promotion/promotion.go	33.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6221   +/-   ##
=======================================
  Coverage   58.05%   58.05%           
=======================================
  Files         499      499           
  Lines       41743    41748    +5     
=======================================
+ Hits        24235    24238    +3     
- Misses      16048    16050    +2     
  Partials     1460     1460           

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[hairyhum]

Does it mean that the full spec would look like this?

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: my-project
  namespace: my-project
spec:
  promotionPolicies:
  - stageSelector:
      name: prod
    autoRollback:
      onFailedPromotions: true|false

[thomastaylor312]

Two small, minor changes needed. Otherwise LGTM

[thomastaylor312]

Shouldn't this be false by default unless set via something like a context option?

[jessesuen]

Yes, it will be false by default. It would only be true if someone/something set the kargo.akuity.io/rollback annotation to be true.

We are building the context object here, determining whether the Promotion is a rollback based on the annotation, which will be set by rollback controller upon rollback.

[thomastaylor312]

I completely misread this on my first pass. This is just fine

[jessesuen]

Does it mean that the full spec would look like this?

Correct.